In the context of implantable medical devices, it has become common to provide a communication link between the implanted device and an external programmer or monitor in order to allow for transmission of commands from the external device to the implanted device and to allow for transmission of stored information and/or sensed physiological parameters from the implanted device to the external programmer. Conventionally, communication between an implanted device and an external programmer has been accomplished by means of a telemetry system which includes transceivers located within the implanted medical device and in an external programmer or monitor, each having a radio transmitter/receiver and one or more antennas.
The implanted device typically includes an antenna located either within the hermetic device housing containing the circuitry, as disclosed in U.S. Pat. No. 4,542,532 issued to McQuilkin, in a plastic header or connector block used to interconnect the device to electrical leads as disclosed in U.S. Pat. No. 5,697,958 issued to Paul et al., or mounted to the device housing as in U.S. Pat. No. 5,861,019 issued to Sun et al., and U.S. Pat. No. 5,720,770 issued to Nappholz et al., all incorporated herein in their entireties. In the past, the programmer or monitor has been provided with a programming head containing an antenna, intended to be placed on or near the patient's body in close proximity to the implanted device. The programming head may be coupled to the external programmer or monitor by means of a cord, as disclosed in U.S. Pat. No. 5,766,232 issued to Grevious et al. The physician handling the programming head has various tasks to perform and positioning of the programming head to a particular location and maintaining that position to maximize received telemetry signal strength is a task that sometimes makes completing the telemetry functions cumbersome. In particular, during an implantation procedure when the IMD is located within a sterile surgical field, the task of positioning of the programming head over the device without breaching the sterile field can become awkward.
Recently, communication systems for implantable medical devices have been proposed in which the programming head is done away with. Communication occurs directly between the programmer or monitor, which may be located some distance from the patient, and the implanted medical device. Such systems are disclosed in U.S. Pat. No. 5,404,877 issued to Nolan et al, U.S. Pat. No. 5,113,869 issued to Nappholz, U.S. Pat. No. 6,240,317 issued to Villaseca et al., and U.S. Pat. No. 6,482,154 issued to Haubrich et al., all of which patents are hereby incorporated herein by reference in their entireties. Long-range telemetry systems, which do not require a programming head to be placed over the IMD, simplify a caregiver's task in programming an IMD, particularly in a crowded clinical, operating room or sterile environment.
Medical device telemetry systems are generally designed for maximum efficiency under implanted conditions, i.e. the dielectric constant and conductivity of human tissue is taken into account when designing the telemetry and antenna system. Programming and interrogation operations, however, are not limited to occurring after device implant. During an implant procedure, telemetry communication may be required for testing procedures or for verifying or customizing initial programmable parameter values before the IMD is implanted. The surgical theater can have multiple RF interferences including other monitoring and medical equipment and RF barriers such as stainless steel surgical carts. These interferences and barriers may make long-range telemetry systems, which have been optimized for operation in the implanted environment, less efficient and reliable when used prior to IMD implantation. An IMD telemetry system is needed, therefore, which takes advantage of the elimination of a programming head but still produces consistently reliable and efficient telemetry transmissions regardless of the operating environment.